A conventional electric device generally includes a trigger, which is electrically connected to the power source such that when the user pulls the trigger, the electric power is provided to the output shaft that is connected to a drill or a saw blade. Nevertheless, there is a potential risk of injury for the users or the object to be machined if the trigger is unintentionally pulled. Once the trigger is pulled, the output shaft immediately rotates at high speed and injury cannot be avoided. Some electric tools have a safety device that simply restricts the trigger from being pulled, if the safety device is unlocked or the user forgot to lock it, the tool can be activated by anyone.
Therefore, it is desired to have a safety device that is cooperated with a brake device. The trigger is pulled to introduce the electric power to drive the output shaft only when the output shaft is braked by operating the brake device.